As in her previous book, Grave Mistake, Ngaio Marsh offers up a lady of a certain age, high-strung and hyperventilating, two ticks short of neurosis. Photo Finish s dead diva, the soprano Isabella Sommita, was widely loathed, so much so that the problem is less a lack of plausible suspects than an embarrassment of options. Though the grand country-house and with it, the country-house murder was history by 1980, when Photo Finish was originally published, Dame Ngaio got around the problem by setting the story on a lavish island estate, cut off from the mainland by a sudden storm. Happily,...